South Eastern Desert Research Articles

An assessment of water resources at Halayib and Shelatine sub regions, southeastern desert, Egypt, using conventional and isotopic approaches

Managing both groundwater and surface water resources is the ultimate aim of the present work. Surface water resources are expressed as runoff water down- percolating due to flash flood events for catchments areas at Halayib and Shelatine sub regions. Hydrologic response of the selected watersheds subjected to single storm event is tested. Base flow source areas and major recharge areas were delineated by field infiltration tests using conventional infiltrometer and the water isotopes of O-18 and H-2. Groundwater resources are represented by two main aquifers; Quaternary aquifers composed of wadi fill deposits resting unconformable over fluviatile sandstone of Um-Barmil Formation of Upper Cretaceous age. Isotopic data (δ18O and δ2H) has revealed the presence of paleowater (highly depleted in delta values) in a hydraulic connection with modern water of Quaternary aquifer (slightly enriched in delta values) receiving direct recharge from the present day precipitation. Accordingly mixing between modern water of Quaternary aquifer with paleowater of Cretaceous aquifer is most likely to occur.

An assessment of water resources at Halayib and Shelatine sub regions, southeastern desert, Egypt, using conventional and isotopic approaches

Managing both groundwater and surface water resources is the ultimate aim of the present work. Surface water resources are expressed as runoff water down- percolating due to flash flood events for catchments areas at Halayib and Shelatine sub regions. Hydrologic response of the selected watersheds subjected to single storm event is tested. Base flow source areas and major recharge areas were delineated by field infiltration tests using conventional infiltrometer and the water isotopes of O-18 and H-2. Groundwater resources are represented by two main aquifers; Quaternary aquifers composed of wadi fill deposits resting unconformable over fluviatile sandstone of Um-Barmil Formation of Upper Cretaceous age. Isotopic data (δ18O and δ2H) has revealed the presence of paleowater (highly depleted in delta values) in a hydraulic connection with modern water of Quaternary aquifer (slightly enriched in delta values) receiving direct recharge from the present day precipitation. Accordingly mixing between modern water of Quaternary aquifer with paleowater of Cretaceous aquifer is most likely to occur.

Microstructural Study and Strain Analysis of Deformed Neoproterozoic Lithologies in the Um Junud Area, Northern Nubian Shield

Estimation of finite strain and microstructural analysis of deformed rocks are keys to better understanding deformational processes and related structures in a variety of scales started from microscopic fabric development to regional-scale structures. In the present work, we carried out the quantitative calculation of strain using the Rf/φ and Fry methods for quartz, feldspar and mafic grains (e.g. biotite and hornblende) from twenty two collected samples for granitic gneiss, amphibolite and hornblende schist samples from the Um Junud area situated in south Eastern Desert of Egypt. Forty four thin sections were prepared and measured by using finite strain methods. The strain data indicate high to moderate ranges of deformation of the amphibolite to granitic rocks. The axial ratios in the XZ section range from 1.74 to 4.37 and 1.50 to 4.46 for the Rf/φ and the Fry methods respectively. The finite strain direction for the long axes displays clustering along N to WNW trend, and shallow WNW plunging in the majority of the studied samples. The short axes are found to be subvertical associated with a subhorizontal foliation. It is concluded that finite strain is of the same order of magnitude for various lithologic units outcropping in the area, and that contacts were formed under semi-brittle to semi-ductile deformation conditions. Thus, the finite strain accumulated during superimposed deformation on a previously nappe structure assemblage, which pointed out that these contacts were created during the accumulation of finite strain. This result is inconsistent with the generally believed that nappe creation in orogens carried out by simple shear deformation.

Comparative study of the drainage basin morphometry extracted from topographic maps and SRTM DEMs: an example from Ghadir watershed, Eastern Desert, Egypt

The drainage network of Wadi Ghadir watershed, southeastern Desert, Egyptwas extracted from topographic maps (1:50. 000), and from the 30 m digitalelevation data (DEM) of the Shuttle Radar Topography Mapping Mission(SRTM). Four topographic sheets were digitized and used for extraction.Archydro function in ArcGIS 10x was utilized for network extraction and formorphometric analysis. Networks derived from topographic sheets and DEMwere considerably coincident. Different morphometric parameters from bothsources were evaluated to examine the accuracy of DEM for hydrologicapplications. Results clarified 6th order streams for both drainage networks withmoderate to high drainage density (D) of 2.51 km.km2 (topographic) and 2.54km.km2 (DEM) reflecting that W. Ghadir drainage basin is impermeable withconsiderable surface runoff. DEM showed higher stream frequency (F) of 4.49than those derived from topographic maps (4.38). Calculated bifurcation ratio(Rb) of streams derived from topographic sheets reached about 3.47 and about4.60 for those derived from DEM. DEM-derived morphometric parametersprovided good and satisfactory information about the catchment characteristicsand revealed accurate watershed delineation confirming high potential ofsurface runoff of the W. Ghadir drainage basin. Finally, SRTM DEM provedadvantageous over the topographic sheets for drainage delineation and basinmorphometry for hydrologic analysis underpinned with the finer spatialresolution and the vertical accuracy.

Utilization of ASTER and OLI data for lithological mapping of Nugrus-Hafafit area, South Eastern Desert of Egypt

Lithological discrimination of Neoproterozoic rocks occupying Nugrus-Hafafit area, South Eastern Desert of Egypt, has been carried out using Operational Land Imager (OLI) and Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) sensors’ imagery data. The applicable processing enhancement techniques include optimum index factor (OIF), band ratioing, principal component analysis (PCA), and minimum noise fraction (MNF) transform. The area comprises varieties of low-grade metamorphosed ophiolitic melange and island-arc rocks, thrusting over high-grade metamorphic gneissic core complexes, and intruded by syn-, late-, and post-tectonic granitoids. The OLI band ratio 6/7 discriminates clearly the ophiolitic serpentinites-talc-carbonate rocks, while 4/5 ratio image is able to separate between mafic and felsic rocks. Moreover, the ASTER band ratio 6/8 is used to distinguish the amphibole-bearing rocks, including amphibolite and hornblende gneiss. The OLI and ASTER second principal component (PC2) images reflect the contrast spectral behavior of ophiolitic melange rocks through visible-near-infrared (VNIR) and shortwave (SWIR) regions. The OLI-PC3 shows the ability to delineate the Fe-rich rocks, including amphibolite and metamafics, while ASTER-PC3 is effective for quartz-feldspathic granites and psammitic gneisses. Visual interpretation and integration of processed data with petrography and field investigation resulted in complete differentiation for the different lithologies and creation of a new detailed geological map of Nugrus-Hafafit area.

Petrogenesis of Zeiatit gabbroic rocks in the Southern Eastern Desert of Egypt: Discrimination of arc-related Neoproterozoic gabbros

The area of Gabal Zeiatit, South Eastern Desert, Egypt represents one of a series of ophiolitic-island arc complexes found within the Arabian–Nubian Shield (ANS). The present study introduces new major, trace, and rare earth element analyses and mineral composition data of gabbroic rocks encountered in this area with the goal of constraining their geotectonic setting. The investigated area consists of two types of gabbroic rocks. The Zeiatit ophiolitic metagabbros (ZMG) are always associated with serpentinites of ophiolitic affinity and were subjected to metamorphism of greenschist to lower amphibolite facies and exhibit tholeiitic affinity and MORB-like characters. Serpentinites and metagabbros are tectonically thrusted over a thick pile of metavolcanic rocks. The Zeiatit intrusive gabbros (ZIG) are related to Egyptian Alaskan-type mafic-ultramafic complexes and intrude the studied ophiolitic rocks and island arc rocks. Geochemical data reveal that both studied gabbroic types originated in sub-arc setting. Mineral chemistry data for the two types of the studied gabbroic rocks indicate that they possess different characteristics. The NiO (<0.15 wt%) and Fo (<83 mol.%) contents of olivine from the investigated ZIG are lower than those of the Egyptian ophiolites. The clinopyroxene composition of the ZIG show arc related cumulate. Geochemically, the ZMG exhibit MORB-like and arc-like signatures as they display Ti/V ratios ranging from 14.52 to 21.09. Such phenomenon of hybrid mixture between island arc tholeiite (IAT) and MORB is generally acknowledged being unique to forearc tectonic regime. Moreover, depleted LREE and HFSE and relatively high CaO in the studied ZMG suggest derivation from Cpx-rich mantle at forearc tectonic setting. The ZIG have Nb/Yb (0.28–1.04) and Th/Yb (0.1–0.42) which are typical for oceanic island arcs. The ZIG are highly depleted in Nb, Ta, and Zr, but enriched in Ba, Pb, Sr, U and Th suggest their derivation from a metasomatized lithospheric mantle source that modified by hydrous fluids derived from the subducting slab in a subduction zone. ZIG have Th/Ta (0.69–2.05) and Ta/Hf (0.16–0.28) indicating that they were mainly derived from partial melting of a depleted mantle source, being mixed with crustal material. The present geochemical and mineralogical studies revealed that, the investigated ZMG are fragment of oceanic lithosphere probably developed in a supra-subduction zone environment and originated by 10–30% partial melting of a spinel lherzolite mantle in a sub-arc (forearc) setting at shallow depth which consistent with the most recent conclusions of the Egyptian ophiolitic metagabbros. However, the investigated ZIG are akin to the Alaskan-type rocks.

Younger Granites and Associated Pegmatites of Gabal El Fereyid – Wadi Rahaba Area, South Eastern Desert, Egypt: Geological and Geochemical Characteristics

Younger Granites and Associated Pegmatites of Gabal El Fereyid – Wadi Rahaba Area, South Eastern Desert, Egypt: Geological and Geochemical Characteristics

Assessment of the natural radioactivity and radiological hazards in granites of Mueilha area (South Eastern Desert, Egypt)

All over the world people are using different hard rocks as ornamental building stones. Information regarding the activity concentration rates for such rocks is very scarce, despite their environmental hazards. Therefore, samples of one of the most spectacular dotted granite were collected from Mueilha area located in the South Eastern Desert, Egypt. The activity concentrations were measured using high-purity germanium detector, and the inductively coupled plasma mass spectroscopy together with the atomic emission spectroscopy techniques were used for the chemical analyses of the samples. Furthermore, the rare earth elements (REEs) of the studied rocks were determined to study the expected economic benefits. It was found that the average concentration values of the radioisotopes (238U, 226Ra, 232Th and 40K) were above the worldwide average in building materials. Distinct variations between the calculated radiological hazards and the corresponding reference values were observed, where some indices had values greater than the world average, e.g. internal hazard index (Hin), annual gonadal dose equivalent (AGDE) and the excess lifetime cancer risk (ELCR), while some others had values lower than the world average, e.g. radium equivalent activity index (Raeq), the gamma representative level index (Iγ) external hazards index (Hex) and the indoor absorbed dose rate (ADR). These variations indicate to the difficulty of using these rocks as a bulk building material.

The use of ASTER data and geochemical analyses for the exploration of gold at Samut area, South Eastern Desert of Egypt

The present study investigates the use of ASTER and geochemical data in the exploration of new gold occurrences in altered granodiorite rocks at Samut area in the South Eastern Desert of Egypt. The mapping approach developed and applied in this study integrates image ASTER and field data sets to produce a map showing the alteration zones within granitoid rocks in the Samut area. Due to the differences in hydrothermal mineral components as well as their intensities and influences on the surrounding rocks, various alteration processes have been occurred within the host granodioritic rocks. Such alteration processes include sericitization, chloritization, silicification, and ferrugination, resulted from the chemical interaction between the host rock minerals and mineral bearing ascending solutions. Each alteration process is characterized by significant minerals. The sericite and altered plagioclase characterize the sericitization process, whereas biotite, muscovite, chlorite, and hornblende minerals are associated with chloritization. However, silicification process is manifested by the quartz veins and fractured quartz grains. The ferrugination process is characterized by the transformation of magnetite to hematite and goethite. The chemical analyses of the unaltered granodiorites yielded Au content between 0.01 and 1.61 ppm, while in the altered granodiorite; Au content is around 0.02 to 14.79 ppm. The presence of gold in the unaltered and altered granodiorite even in a low percentage, but in huge tonnages gives an importance and makes the study area worthy of gold exploration and possible exploitation and hence international propagation. The Samut district is made up of intermediate to acidic metavolcanics intruded by a hornblende granodioritic pluton and cut by acidic dykes and quartz veins and veinlets. The associated hydrothermal activity with the plutonic intrusion led to the occurrence of promising alteration zones for gold in the granodiorite.

Reappraisal of the kinematic history of Nugrus shear zone using PALSAR and microstructural data: implications for the tectonic evolution of the Eastern Desert tectonic terrane, northern Nubian Shield

Nugrus shear zone (NSZ) is a NW-trending semiductile-semibrittle high-strain zone exhibiting obvious sinistral sense of shear. It is regarded by some workers to represent the boundary between the Central Eastern Desert (CED) and South Eastern Desert (SED) of Egypt. A variety of Neoproterozoic lithologies are remarkably affected by the NSZ, encompassing high-grade gneisses, metavolcanics and metavolcaniclastics, gneissose granite, and ophiolitic melange. Visual interpretation and automated lineament extraction have been applied on the local sigma-filtered level 1.5 PALSAR data. Results of directional filtering and line algorithm techniques support the dominance of NW and NE structural trends in the study area. Microstructural and finite strain analyses have been done for the oriented samples of gneisses, metavolcanics, metavolcaniclastics, and gneissose granite using CSS, Fabric 8, and EllipseFit software. The Rf/ϕ and Fry methods demonstrate that the strain ratios of the collected samples are closely compatible and consistent. The core of Hafafit culmination gave 1.5 strain ratio with top-to-the-NW sense of shear, whereas the two rims show 1.7 strain ratio with top-to-the-NE sense of shear. Samples collected along the flanks of Wadi Nugrus show the two types of shear but the NW is dominant with 1.8 strain ratio and sinistral sense of shear, whereas those collected from Wadi Abu Rashid and Wadi Sikiat display 1.4 strain ratio with dextral sense of movement. Finite strain results along with field relations and observations prove that the NSZ and environs experienced a prolonged tectonic history involving at least three deformations (Dl, D2, and D3). D1 phase involves NE-SW shortening and is documented by large-scale NW-trending, NE-dipping, imbricate thrust sheets with NE plunging stretching lineation. D2 was a transpressional phase (660–645 Ma), coeval with the Najd Shear System (NSS), and expressed by the NW- to NNW-trending, steeply dipping, strike-slip shear zones with frequent subvertical foliation and subhorizontal lineation. Exhumation of gneissic domes in Hafafit area was related to this phase. The D3 phase (645–540 Ma) was responsible for the formation of NE-oriented shear with dextral sense of movement. Whether the NW and NE shears are conjugate pairs or not will be a matter of much discussion.

Biostratigraphy and paleogeography of the southeast desert phosphorites of Jordan

Three sections from the Al-Hisa Phosphorite Formation (AHP) were measured in the southeastern desert of Jordan: Batn El-Ghoul, Nagb Etayyeg, and Zgaimat Al-Hasah. A fourth section, Wadi Arfa, is added from a previous work. The three sections differ from the typical AHP Formation in central Jordan by having highly reduced thicknesses, omission/non-deposition of the underlying formations, rarity of fossils, abundant sand, and their stratigraphic ages. A Paleocene-Early Eocene age, based on calcareous nannofossils, has been assigned to the AHP Formation of the sections studied in the southeast desert. This Paleocene-Early Eocene age is younger than the Early Maastrichtian age of the AHP deposits in central Jordan. The published ages of the phosphorite deposits in the eastern Mediterranean countries suggest a younging to the east due to an interplay between paleodepositional environments and plate tectonics (paleohigh formation). The minor phosphorite deposits of Turkey and Iran are not involved in the discussion because they were not part of the Afro-Arabian Plate or the later Arabian Plate. The abovementioned differences between the southeastern desert phosphorites and the central Jordan deposits are here explained by the formation of paleohighs on the Neo-Tethys seafloor during the Late Cretaceous-Eocene. These include the Sirhan Paleohigh where the southeast desert phosphorites were deposited. The formation of the highs was due to the compression associated first, with the subduction of the Afro-Arabian Plate, below the Eurasian Plate and later with their collision.

Equatorial paleolatitude for Northeast Africa in the Late Triassic: paleomagnetic study on the Gezira and Bir-Umhebal [229–223 Ma] ring complexes, Southeastern Desert, Egypt

Two Late Triassic alkaline ring complexes in the Southeastern Desert of Egypt: the Gezira [229 ± 5 Ma, K/Ar biotite] and Bir-Umhebal [223 ± 9 Ma, Rb/Sr], were paleomagnetically studied to determine the paleo-latitude position of Northeast Africa during the Late Triassic just before the Jurassic dispersion of Pangaea. The initial isothermal remanent magnetization [IRM] study was followed by the progressive thermal demagnetization of all samples to verify the characteristic natural remanent magnetic directions of both complexes. The analysis revealed that: (i) the magnetite-dominated sites generally, had dual-polarity, bi-vectorial with shallow sub-equatorial N–S to NNW–SSE anchored remanent magnetic component, while (ii) the hematite/goethite sites were characterized by normal polarity, bi-vectorial decay with a northward anchored component fluctuating around zero inclination. Based on their thermal demagnetization behavior, only the magnetite-dominated sites were considered as representing the average Late Triassic paleomagnetic field in the study areas during cooling of the studied complexes. The mean paleomagnetic north poles of the isolated characteristic component using the principal component analysis [PCA] for each complex were: (i) the north poles of Gezira Complex [22.3°N/33.6°E] was at (54.6°N/226.2°E, Dp/Dm= 5°/9°); (ii) the north poles of Bir-Umhebal Complex [23.75°N/28 33.3°E] was at (56.4°N/236°E, Dp/Dm= 3°/6°), and (iii) the mean north pole of both complexes [23°N/33.5°E] was at (56°N/231°E, Dp/Dm = 3°/6°). The obtained Late Triassic [Late Carnian-Early Norian] paleomagnetic poles for the two ring complexes of Egypt show reasonable consistency with their synchronous African poles as well as poles rotated from the main tectonic units to the Northeast Africa using appropriate Euler pole parameters. These poles reveal that in the Late Triassic:The obtained Late Triassic [Late Carnian-Early Norian] paleomagnetic poles for the two ring complexes of Egypt show reasonable consistency with their synchronous African poles as well as poles rotated fromthe main tectonic units to the Northeast Africa using appropriate Euler pole parameters. These poles reveal that in the Late Triassic: (i) the northern part of Africa was in Equatorial paleo-latitudes with Northeast Africa lying just south the Equator. Cairo [Now at 30°N] was at −4.4° to −1° paleo-latitude; (ii) the Azimuth of the African Plate was between N and 37 NNE about 9° to14° clockwise to its present-day azimuth.

Evolution of monogenetic rift-related alkaline magmatism in south Egypt: Insight from stratigraphy, geochronology, and geochemistry of the Natash volcanics

The Mesozoic Natash volcanics are rift-related monogenetic volcanic complex that erupted in south Eastern Desert of Egypt. The architecture of their building has evolved through three phases namely: (1) tuff cone consisting of explosive -dominated pyroclastics that stand for an intensity eruption peak; (2) the effusive lava-conquered phase, characterized by prevalent basalt-trachyte-rhyolite fissure eruptions; and (3) late-stage subvolcanic plugs/domes. The first phase began with the emplacement of spatter-rich ignimbrites followed by grain-supported lapilli-tuffs and hyaloclastics in a shallow-water environment (phreatomagmatic phase) with a vent-opening phase. This initial phase is followed by deposition of clast-supported conglomerates of lahar facies that represent significant erosional period, separating the pyroclastics and effusive phases. The second phase comprises multiphases displaying compositional stratification (primitive beneath evolved) of pahoehoe Hawaiian and rubbly vulcanian lavas, overlying the pyroclastic deposits. The third phase is the youngest and comprises plugs of aphyric trachytes. The volcanics occasionally have vesicle sheets, cylinder-elongate vesicles, gas blister, and inflation clefts, reflecting degassing, rupturing, brecciation/quenching history, and pressurized flows. U-Pb zircon ages from two samples of trachyte volcanics gave concordant age of 92 ± 0.9 Ma. One trachyte plug yielded concordant age of 86.6 ± 1.3 Ma. These ages represent two events belonging to the major Senonian volcanic activities. The investigated volcanics have alkaline affinity and display a continuous composition ranging from basalt to trachyte and rhyolite. Their chemical compositions display linear, curvilinear, and scattered trends on the Harker diagrams matched with the petrographic data and reflect comagmatic genesis for the entire sequence. Crystal fractionation of olivine + pyroxene + plagioclase + Fe-Ti oxides + apatite plays a role in the volcanic evolution. The origin of the mafic rocks is derived from deep mantle source in the garnet facies via low degree of partial melting. Such magma source is affected by fluid-rich metasomatism generated by dehydration subducted crust on the EM I, EMII, and HIMU mantle reservoir during Neoproterozoic time. The basalt-trachyte-rhyolite suites and their pyroclastics from the Natash area, together with Mesozoic alkaline volcanics from the surrounding terrains in Africa, constitute a remnant of extensive magmatisms, having large extension, high eruption rate, and OIB-type chemical composition.

On the relative timing of listwaenite formation and chromian spinel equilibration in serpentinites

Ultramafic rocks exposed at the Earth's surface generally record multiple stages of evolution that may include melt extraction, serpentinization, carbonatization, and metamorphism. When quantitative thermometry based on mineral chemistry is applied to such rocks, it is often unclear what stage of their evolution is being observed. Here, in peridotites with extensive replacement of silicate minerals by carbonates (listwaenites), we present a case study that addresses the timing of carbonate formation relative to closure of exchange reactions among relict primary minerals. Massive and schistose serpentinized peridotites of Neoproterozoic age outcrop at Gabal Sirsir, South Eastern Desert, Egypt (northwestern corner of the Arabian-Nubian Shield or ANS). Petrography, bulk composition, and mineral chemistry are all consistent with a strongly depleted mantle harzburgite protolith for the serpentinites. Bulk compositions are low in Al_2O_3 and CaO and high in Mg# [molar Mg/(Mg+Fe) = 0.89–0.93]. Relict spinel has high Cr# [molar Cr/(Cr+Al)] and low Ti, while relict olivine has high Mg# and NiO contents. Based on compositions of coexisting relict olivine and chromian spinel, the protolith experienced 19 to 21% partial melt extraction. Such high degrees of partial melting indicate a supra-subduction zone environment, possibly a forearc setting. Along thrust faults and shear zones, serpentinites are highly altered to form talc-carbonate rocks and weathering-resistant listwaenites that can be distinguished petrographically into Types I and II. The listwaenitization process took place through two metasomatic stages, associated first with formation of the oceanic crustal section and near-ridge processes (∼750–700 Ma) and subsequently during obduction associated with the collision of East and West Gondwana and escape tectonics (∼650–600 Ma). In the first stage, Mg# of chromian spinel in the serpentinites continuously changed due to subsolidus Mg–Fe^(2+) redistribution, while the Mg# of chromian spinel in the Type I listwaenites was frozen due to the absence of coexisting mafic silicates. During the second stage, the Type II listwaenites formed along shear zones accompanied by oxidation of relict chromian spinel to form ferritchromite and Cr-bearing magnetite in both serpentinites and listwaenites. The high Cr# of chromian spinel relics in both serpentinites and listwaenites preserves primary evidence of protolith melt extraction, but divalent cations are more easily mobilized at low temperature. Hence, relict chromian spinel in listwaenites shows significantly higher Mg# and lower MnO than that in serpentinite, suggesting that nearly complete alteration of ultramafic rocks to form listwaenite took place prior to re-equilibration between chromian spinel and the surrounding mafic minerals in serpentinites. Furthermore, the ferritchromite in the serpentinites has higher Mn content (1.1–2.1 wt%) than that in the listwaenites (0.6–0.9 wt%), indicating its formation after carbonatization since carbonate minerals are a favorable sink for Mn.

Provenance studies of Kalabsha kaolin deposits, Egypt: a petrographical and geochemical approach

The present study focuses on the kaolin deposit in Kalabsha area south Western Desert of Egypt in an attempt to determine its possible source, tectonic setting, and weathering history by means of integrated petrographical and geochemical approaches. The petrographical study was worked by microscopic investigation and supported by X-ray diffraction analysis. X-ray fluorescence and inductively coupled plasma-mass spectrophotometry methods were used for the determination of the bulk elemental composition. Mineralogical analysis revealed that kaolinite is the main clay mineral component indicating a severe chemical weathering of Al-rich source rocks and complete leaching under warm, semiarid climatic conditions. The nonclay minerals are represented by quartz, iron oxides and hydroxides, Ti-bearing minerals, and zircon. Geochemical data show a prevalence of SiO2 and Al2O3 and enrichment of Hf, Nb, Ta, Th, U, and Zr that support the kaolinitic nature of the deposits and their derivation from a felsic granitic terrain. The high values of the chemical index of alteration and the lower values of the index of compositional variability also suggest an intensive weathered source area and the geochemical maturity of the sediments. Other relevant geochemical discriminant functions and plots reveal felsic igneous parent rock for the kaolin deposits. Q-mode hierarchical cluster analysis combined with the normalized rare earth element patterns played a crucial role in unraveling the origin of the studied deposits. The results show that the most probable source rock of the Kalabsha kaolin deposits is the intense weathering of relatively proximal Adara Adatalob granites and their similar rock types in the Arabian-Nubian Shield from the south Eastern Desert of Egypt.

Stratigraphy and facies development of the pre-Cenozoic sediments in southern Egypt: a geodynamic approach

The study of the geology of southern Egypt, in-between the Red Sea and the Libyan borders, south of latitude 24°30′N reveals a succession of the Precambrian Arabo–Nubian Shield along the Red Sea coast overlain by Paleozoic–Mesozoic sediments. The Paleozoic section in the study area is well developed in three sub-basins, namely, Uweinat–Gilf, South Nile, and Etbai. Paleozoic sediments are well developed in the three sub-basins mostly sandstones of Cambrian overlain by glaciogene sediment conglomerates at base namely Gabgaba Formation and by the Naqus Sandstone at top. The tectonic events during the Early Paleozoic Caledonian Orogeny are marked by several unconformities and tectonic uplift and down faulting expressed in the many faults in the Uweinat–Gilf and South Nile sub-basins. The Carboniferous is well-developed sandstones in the three studied sub-basins. The glaciation at the Permian is reflected in sea-level fall, hence continental sediments are well developed in many parts of Egypt—a phase of the Hercynian Orogeny. Volcanics are very well common in the study areas ranging in age from 48 to 34 Ma at Uweinat and Gebel El-Asr. Vulcanicity continued during the Paleozoic and Mesozoic at the Triassic of Nasab El-Balgum and in the south Western Desert, the south Eastern Desert, and Etbai area. The highly seismic conditions in southern Egypt continued up to very recent times where tremors were noticed in the 80s and 90s of the last century pointing to very unstable area.

Petrology, geochemistry, radioactivity, and M–W type rare earth element tetrads of El Sela altered granites, south eastern desert, Egypt

The southern part of the Eastern Desert of Egypt—about 30 km southwest of Abu-Ramad city—is mainly covered by ophiolitic rocks (Sul Hamed), island arc assemblage, younger granites (muscovite granites of Qash Amer and two mica granites of El Sela), and various acidic and basic dikes. Field, petrological, and geochemical studies indicate that the El Sela shear zone has been subject to hydrothermal and supergene alteration such as kaolinization, albitization, sericitization, and hematitization. It is invaded by quartz ENE–WSW veins associated with hydrothermal alteration accompanied by radioactive mineralization. The investigated younger granitic rocks had very low contents of compatible elements, such as Cr, Ni, and Co; and high contents of incompatible elements, such as Zr, and large ion lithophiles, such as Sr, especially in the El Sela shear zone. Major oxide and trace element analyses revealed calc-alkaline affinity and peraluminous character. These highly differentiated granitic rocks’ lower Zr/Hf and higher Y/Ho than the normal ratio are consistent with hydrothermal alteration. Most samples had rare earth element (REE)-patterns with an M-type tetrad effect in the first and fourth segments and a W-type tetrad in the third segment. The average ∑REE in the studied granites was lower than the world granite average; the ratio of light to heavy REEs greater. The main radioactive, uranium-bearing, and uraniferous Fe and Mn minerals are uranothorite, autunite, uranophane and autunite as compounds, kasolite, columbite, xenotime, uranophane-bearing zircon and jarosite, silver-bearing pyrite, hematite, and autunite-bearing pyrolusite.

Trace elements and isotope data of the Um Garayat gold deposit, Wadi Allaqi district, Egypt

Trace element composition of sulfides and O, C, Sr and S isotopic data are assessed to constrain the evolution and potential fluid and metal sources of the Um Garayat gold deposit. Ore microscopy and BSE investigations of quartz veins show blocky arsenopyrite and pyrite replaced in part by pyrrhotite, chalcopyrite, sphalerite, galena, and gersdorffite. Free-milling gold occurs commonly in close association with the late sulfides, and along fractures in pyrite. On the other hand, recrystallized pyrite is disseminated in host metavolcaniclastic/metasedimentary rocks that commonly contain carbonaceous material. In situ LA-ICP-MS analysis of sulfides shows the recrystallized pyrite enriched in most trace elements, while blocky pyrite contains only some traces of arsenic. Detected concentrations of gold (up to 17 ppm) were only reported in arsenopyrite disseminated in quartz veins. The δ34S values of blocky pyrite and pyrrhotite in quartz veins define a narrow range (1.6 to 3.7‰), suggesting a homogenous sulfur source which is consistent with the dominantly mafic host rocks. The recrystallized pyrite has a distinctive sulfur isotope composition (δ34S − 9.3 to − 10.6‰), which is rather comparable to diagenetic sulfides. Hydrothermal carbonate in quartz veins and wallrock have nearly constant values of δ18O (10.5 to 11.9‰) and δ13C (− 4.2 to − 5.5‰). Based on constraints from mineral assemblages and chlorite thermometry, data of six samples indicate that carbonate precipitation occurred at ~ 280 °C from a homogenous hydrothermal fluid with δ18OH2O 4.4 ± 0.7‰ and δ13C = 3.7 ± 0.8‰. Strontium isotope values of two samples (87Sr/86Sr = 0.7024 and 0.7025) are similar to the initial 87Sr/86Sr ratios of island arc metabasalts (~ 710 Ma) in the South Eastern Desert. The generally homogenous sulfur, C, O, Sr isotope data are suggestive of metamorphogenic fluids, likely produced from dominantly mafic volcanic rocks at the greenschist–amphibolite facies transition.

Formation of corundum and associated mineral zones in the hybrid ultramafic-pegmatite association of the Neoproterozoic Hafafit core complex, South-Eastern Desert, Egypt

Unusual series of hybrid metasomatic mineral zones are well developed when the granitic pegmatite veins cross-cut through ultramafic rocks at the Hafafit complex, South Eastern Desert of Egypt. Two groups of mineralogical zones are developed; the first group related to the serpentinized ultramafic rocks (peridotite-related zones) comprises anthophyllite-, actinolite- and vermiculite-bearing zones, whereas the second group related to the pegmatite veins (pegmatite-related zones) comprises hercynite- and corundum-bearing zones. Tourmaline-rich zone only occurs when the pegmatite veins come in contact between ultramafic rocks and biotite-rich granitic gneiss. The mineral assemblages, bulk rock geochemistry and in situ mineral chemistry suggest a metasomatic origin for the hybrid zones. The mineral assemblages: corundum + margarite ± Ca-plagioclase, hercynite + corundum + garnet ± chlorite, and anthophyllite + actinolite + enstatite, in addition to the constrained garnet-biotite/phlogopite geothermometer, and the higher tourmaline XMg, strongly indicate amphibolite facies metamorphism for the ultramafic-pegmatite hybrid zones. The constrained temperature ranges between 500 and 700 °C and a pressure around 7 kbars, with pronounced increases of metamorphism from the outermost zone in the serpentinized ultramafic ongoing to the pegmatite mineral zones. Juxtaposition of two contrasting rock types (highly reactive hot SiO2-, alkali-rich melt and cool silica-deficient ultramafic rocks) side by side would results in an intense contact bimetasomatic elemental exchange. The SiO2, H2O and alkalies would be offered by pegmatite melt, while MgO, FeO and CaO were supplied by serpentinized ultramafic rocks. The small volume of pegmatite melt relative to the ultramafic rocks would be easily desilicated by SiO2 diffusion into the ultramafic rocks to form the monomineralic SiO2-rich minerals in the peridotite-related zones. Consequently, Al2O3 would be concentrated in the residual melt to form corundum and other Al-rich mineral phases in the pegmatite-related zones. The small size of pegmatite veins and refractory nature of the ultramafic rocks could be the reasons precluding the formation of colored gem corundum in the Hafafit complex. Restricted occurrence of tourmaline-rich zone at the ultramafic-granitic gneiss contact is attributed to the diffusion of B-rich fluids generated from the leaching of biotite-rich granitic gneiss.

Leaching and Precipitation of Thorium Ions from Cataclastic Rocks, Abu Rusheid Area, South Eastern Desert, Egypt

THE LEACHING of thorium from representative samples collected from Abu Rusheid area, south Eastern Desert, Egypt using sulphuric acid has been studied. Factors affecting the leaching of thorium were investigated such as, acid type, S/L ratio, H2SO4 concentration, leaching time, temperature and grain size. The best conditions for leaching of thorium were, H2SO4 acid as the best acid, S/L ratio of 1:5, 3.0 M H2SO4, 2.0 hour of leaching time, -200 mesh size at 90°C. After leaching, the mixture was filtrated then divided into two parts the leach liquor and the residue. The leach liquor was adjusted at pH 1.0 by ammonia solution and addition 10 % oxalic acid. The precipitate obtained was filtrated and dried at 120oC for 1 hour. The obtained precipitate showed 91.60 % of thorium content when using 3.0 M H2SO4 acid. The quality of the precipitate was confirmed by XRF